1. Field of the Invention
The invention relates to the field of implantable cardiac stimulation devices and more particularly to evaluating one or more measures of mechanical physiologic activity for individually optimizing or adapting therapy delivery provided by an implantable cardiac stimulation device.
2. Description of the Related Art
Numerous people suffer from physical ailments affecting their heart function. Patients having diseased myocardium often exhibit impairment of the normal physiologic conduction system, myocardial stunning, hibernation, and/or myocardial necrosis. Of these symptoms, myocardial stunning, hibernation, and necrosis generally lead to hypocontractility of the cardiac muscle. Many patients also exhibit reduced cardiac output as a secondary symptom of a lack of myocardial contractility, impaired conduction, and/or deficiencies in the synchronicity of cardiac depolarization/repolarization. These factors generally result in impaired systolic and/or diastolic function which results in the commonly named congestive heart failure (CHF) or simply heart failure (HF).
Accordingly, a variety of therapies, including therapies automatically provided by therapeutic devices, have been developed and continue to be further developed for treatment of patients, including patients suffering from HF. One particular category of therapy which has been developed is provided by implantable cardiac stimulation devices. Such cardiac stimulation devices are frequently configured to be implanted in order to provide long term automatic monitoring of the patient's condition and to generate and deliver therapeutic cardiac stimulation as indicated. Implantable cardiac stimulation devices have been developed to monitor and provide therapy independently to multiple locations of the patient's heart, including multiple chambers of the patient's heart.
One particular category of implantable cardiac stimulation devices includes the ability to monitor activity in and selectively deliver therapy to both of the patient's ventricles. This is frequently referred to as bi-ventricular or bi-V therapy. Implantable cardiac stimulation devices configured for bi-ventricular stimulation can be further configured to provide cardiac resynchronization therapy (CRT). CRT refers to modes of therapy which strive to restore a more closely normal synchronization between the patient's right and left ventricles.
While CRT is as yet not effective with all patients suffering from HF, for many HF patients, CRT can improve the overall pumping effectiveness of an HF patient and thereby improve their quality of life. In at least certain patients, CRT can at least partially compensate for conduction/stimulation deficiencies to thereby improve synchronization of the electrical stimulation of the myocardium and to at least partially compensate for myocardial tissue having impaired contractility.
While CRT has been shown to provide valuable benefits to certain HF patients, there remains a sizeable portion of the HF population that has been non-responsive or at best less responsive to existing CRT systems and algorithms. Thus, it will be appreciated that there exists needs for improved systems and methods of delivering cardiac therapy both to improve the efficacy for patients who have exhibited positive response, as well as to provide new types of therapy for those patients who have exhibited less beneficial response.
HF, for example, is often a progressive condition and can manifest in different disease conditions. Evaluation of the progression of disease conditions and the particular physiologic manifestations in an individual patient are important to improving therapy delivery, particularly where the condition is progressing and/or involves localized impairment. Thus, there is an ongoing need for systems of more accurately evaluating a patient's condition and providing appropriate indications for any changes in therapy. It would be beneficial to provide improved systems and methods of providing therapy that would be generally compatible with existing hardware platforms. It would be further advantageous to provide innovative systems and methods of providing therapy that would be compatible with improved hardware platforms.